1. Field of the Invention
The present invention relates generally to a mobile communication system supporting a Multimedia Broadcast/Multicast Service (MBMS), and in particular, to an apparatus and method for transmitting and receiving control information for supporting an MBMS service.
2. Description of the Related Art
Currently, due to the development of communication technology, services provided in a Code Division Multiple Access (CDMA) mobile communication system are developing into Multicasting/Multimedia Communication for transmitting not only the existing voice service data but also mass data such as packet data and circuit data.
In a Universal Mobile Telecommunication Service (UMTS) system, which is a 3rd generation (3G) mobile communication system employing Wideband Code Division Multiple Access (WCDMA) technology based on Global System for Mobile communications (GSM) and General Packet Radio Services (GPRS), Broadcast/Multicast Service in which the same data stream is provided from one data source to a plurality of user equipments (UEs) is supported in order to support the Multicasting/Multimedia Communication. The Broadcast/Multicast Service can be classified into Cell Broadcast Service (CBS), which is a message-oriented service, and Multimedia Broadcast/Multicast Service (hereinafter referred to as “MBMS service”) for supporting multimedia data including real-time image and voice, still image, and text.
FIG. 1 is a diagram schematically illustrating a network configuration for providing an MBMS service in a mobile communication system. A broadcast/multicast-service center (BM-SC) 110 is a source that provides an MBMS stream, and the BM-SC 110 schedules an MBMS service stream and sends the scheduled MBMS service stream to a transit network (NW) 120. The transit network 120 is a network that exists between the BM-SC 110 and a serving GPRS support node (SGSN) 130, and sends the MBMS service stream provided from the BM-SC 110 to the SGSN 130. The transit network 120 is comprised of a gateway GPRS support node (GGSN) and an external network.
The SGSN 130 receiving an MBMS service stream via the transit network 120 controls an MBMS service for the subscribers, i.e., UEs 161, 162, 163, 171 and 172, desiring to receive the MBMS service. For example, the SGSN 130 manages MBMS service accounting data for each of the subscribers, and selectively transmits MBMS service data to an associated radio network controller (RNC) 140. In addition, the SGSN 130 generates and manages a service context for the MBMS service and sends a stream for the MBMS service to the RNC 140.
The RNC 140 transmits the MBMS service stream to Node Bs 160 and 170 controlling the cells where the UEs 161, 162, 163, 171 and 172 requesting an MBMS service are located, among the Node Bs managed by the RNC 140 itself. The RNC 140 and the Node Bs 160 and 170 constitute a UMTS terrestrial radio access network (UTRAN).
A cell#1 belonging to Node B1 160 desiring to receive a particular MBMS service includes UE1 161, UE2 162 and UE3 163, and a cell#2 belonging to Node B2 170 includes UE4 171 and UE5 172. Herein, the term “cell” has a meaning similar to that of the term “Node B.” In this case, the RNC 140 controls radio channels set up between Node Bs 160 and 170 and UEs 161, 162, 163, 171 and 172 in order to provide the MBMS service. As illustrated in FIG. 1, one radio channel is established between one Node B, e.g., Node B1 160, and UEs 161 to 163 belonging to the Node B1 160 in order to provide an MBMS service.
In order to receive an MBMS service, UEs 161, 162, 163, 171 and 172 first acquire control information for an MBMS transport channel (MTCH), for transporting an MBMS service data stream. The control information includes code information for a code channel to which the transport channel is mapped and information on a service identity (ID) for the MBMS service, and is transmitted over an MBMS control channel (MCCH), a separate logical channel distinguished from the transport channel.
The control information for the MBMS service as well as the MBMS service data must be transmitted on a multicast basis. In particular, radio bearer (RB) information for an MBMS service is available for all UEs desiring to receive the MBMS service. However, if an MCCH, like other logical channels, is mapped to all transport channels before being transmitted, the UEs must decode all logical channels in order to receive the MCCH, causing an increase in its load. Thus, there is a demand for technology for enabling UEs to rapidly and simply receive control information for an MBMS service in order to rapidly receive the MBMS service in a cell.